1. Field of the Invention
The present invention relates to an optical-disk drive device which applies light to an optical disk, and records or/and reproduces information.
2. Description of the Related Art
Conventionally, for example, as disclosed in Japanese Unexamined Patent Publication No. 10-222-864 specification, there is proposed an optical-disk drive device which can record and reproduce information at two numerical apertures (or NAs).
FIG. 15 shows a conventional optical-disk drive device, which is described in that specification. As shown in FIG. 15, the optical-disk drive device includes: several light receiving-and-emitting units 131, 132; a polarization beam splitter 135 which is a means for allowing optical paths to join together; a collimating lens 139; a half mirror 143 which is a means for allowing a luminous flux to branch off; a single photo-detector 144; and an objective lens 140. The light receiving-and-emitting unit 131 is provided with a light-emitting element 133 and a first light-receiving element 161. The light receiving-and-emitting unit 132 is provided with a light-emitting element 134 and a first light-receiving element 162. The photo-detector 144 is provided with a second light-receiving element 151. The light-emitting element 133 and the light-emitting element 134 are not simultaneously driven. Only either of them is driven to emit light.
The light-emitting element 133 is driven when an optical disk (i.e., a record medium) 141 is driven. At this time, a luminous flux 136 which has been emitted from the light-emitting element 133 passes through the polarization beam splitter 135. Then, it is transformed into a substantially parallel beam by the collimating lens 139. The luminous flux 136 which has been transformed into the substantially parallel beam is focussed on the optical disk 141 by the objective lens 140. The light which has been reflected by the optical disk 141 is traced back to the light receiving-and-emitting unit 131, through the optical path which it had passed along. Inside of the light receiving-and-emitting unit 131, the reflected light is led to the first light-receiving element 161 by a hologram element (not shown), and then, it is received.
The light-emitting element 134 is driven when an optical disk (i.e., a record medium) 142 is driven. At this time, a luminous flux 137 which has been emitted from the light-emitting element 134 is reflected and turned at a right angle by the polarization beam splitter 135. Then, it passes along the same optical path as that of the luminous flux 136. The reflected light 137 is transformed into a substantially parallel beam by the collimating lens 139 and is focussed on the optical disk 142 by the objective lens 140. The light which has been reflected by the optical disk 142 is traced back to the light receiving-and-emitting unit 132, through the optical path which it had passed along. Inside of the light receiving-and-emitting unit 132, the reflected light is led to the first light-receiving element 162 and is received.
The half mirror 143 reflects a part of the parallel beam from the collimating lens 139 and transmits the rest. The beams of light of the luminous flux 136 and the luminous flux 137 which have been reflected by the half mirror 143 are both received as the front light by the single second light-receiving element 151 inside of the photo-detector 144. A signal which is outputted from this photo-detector 144 is fed back to each drive circuit of the light-emitting elements. Thereby, the output of each of the light-emitting element 133 and the light-emitting element 134 can be kept constant.
As described above, a signal can be recorded on the optical disk 141 or the optical disk 142, or a signal which is recorded on the optical disk 141 or the optical disk 142 can be reproduced.
However, according to the above described conventional configuration, as shown in FIG. 16, only the middle part of each of the luminous flux 136 and the luminous flux 137 is detected by the second light-receiving element 151. If the light-emission pattern of each light-emitting element 133, 134 varies according to a change in the ambient temperature, a change in their light-emission power or the like, that can break off the proportional correlation between the light-emission quantity of each light-emitting element 133, 134 and the light-receiving quantity of the second light-receiving element 151. In such a case, a disadvantage may arise in that the quantity of light cannot be precisely controlled.
In addition, accurate light-quantity control may also be hindered in the case where a single optical-disk drive device makes a recording and a reproduction at several numerical apertures. Even if the total quantity of a luminous flux is designed to be detected at a specific numerical aperture by the second light-receiving element 151, then only a part of the luminous flux, or further, an unnecessary luminous flux, may be detected at another numerical aperture.